Image sensing apparatus, method of controlling image sensing apparatus and image recording apparatus, and method of designing optical system

ABSTRACT

An image sensing apparatus which has an optical system, the focal length of which is variable, and an image sensing element that converts an image formed by the optical system into an electrical signal, and can sense and record a moving image and still image, includes a focal length detection circuit for detecting the focal length of the optical system, and a control unit for inhibiting recording of the still image in accordance with the focal length detected by the focal length detection circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/299,668,filed Dec. 13, 2005 now U.S. Pat. No. 7,535,500; which is a divisionalof application Ser. No. 09/663,543, filed Sep. 15, 2000, now U.S. Pat.No. 6,987,532, the entire disclosure of which is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to an image sensing apparatus, method ofcontrolling an image sensing apparatus and an image recording apparatus,and a method of designing an optical system used and, more particularly,to an image sensing apparatus, method of controlling an image sensingapparatus and an image recording apparatus, and a method of designing anoptical system when a multi-pixel image sensing element is used.

BACKGROUND OF THE INVENTION

Conventionally, image sensing apparatuses which can record both stillimage and moving images have been proposed. For example, and imagesensing apparatus that integrates a video camera and tape recorder, andcan record a moving image and still image on a single tape, and an imagesensing apparatus which records a moving image on a tape and records astill image on another recording medium such as memory, are known.

In recent image sensing apparatuses, an image sensing element has alarger number of pixels. However, an optical system including lensesbecomes larger with increasing number of pixels of the image sensingelement. Such increase in size of the optical system is to achieve anoptical resolution corresponding to the increase in the number ofpixels, and even when the size of the image sensing area (image size) ofthe image sensing element remains the same, an optical system must bedesigned so as to correspond to such multi-pixels. Especially, in stillimage sensing, an image sensing element which has a high pixel densityapproaching a silver halide camera has been put into practicalapplications, and an image sensing apparatus that can record both stilland moving images described in the prior art is beginning to adopt suchmulti-pixel image sensing element.

However, moving images still use the video format such as NTSC thatcomplies with an existing moving image sensing scheme, and such imageneed not be recorded at such high resolution that exhibits the resolvingpower of the multi-pixel image sensing element.

Therefore, upon examining an image sensing apparatus which uses amulti-pixel image sensing element and can record both still and movingimages, such system can improve the resolution of a still image comparedto the conventional image sensing apparatuses, but has a bulky opticalsystem, and has a resolution of a moving image as low as theconventional apparatus.

Furthermore, in a so-called zoom lens as an optical system that can varythe focal length, the size of the optical system increasesconspicuously, and such tendency is considerable with increasingvariable focal length ratio (zoom ratio).

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its object to provide an image sensing apparatuswhich assures good balance between the size of an optical system andimage quality in correspondence with conditions such as the use purposeof the image sensing apparatus, the required resolution of a sensedimage, the size of the image sensing apparatus, and the like, an imagesensing method, and a method of designing an optical system used in theimage sensing apparatus.

According to the present invention, the foregoing object is attained byproviding an image sensing apparatus comprising an image sensing elementthat converts an optical image of an object passed through an opticaltransparent member to an image signal, and an image processing devicethat performs moving image signal processing for processing the imagesignal converted by the image sensing element as a moving image signaland still image signal processing for processing the image signal as astill image signal, wherein, when the still image signal processing isto be executed, the signal processing device performs predeterminedcontrol in response to movement of the optical transparent member to apredetermined position, the predetermined control being not performedwhen the moving image signal processing is to be executed.

According to the present invention, the foregoing object is alsoattained by providing an image sensing apparatus comprising an imagesensing element that converts an optical image of an object passedthrough an optical transparent member to an image signal, and an imageprocessing device that performs first signal processing for obtaining animage signal of a first resolution from the image signal converted bythe image sensing element and second signal processing for obtaining animage signal of a second resolution which is higher than the firstresolution from the image signal, wherein, when the second signalprocessing is to be executed, the signal processing device performspredetermined control in response to movement of the optical transparentmember to a predetermined position, the predetermined control being notperformed when the first signal processing is to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing an image sensing apparatus comprising animage sensing element that converts an optical image of an object passedthrough an optical transparent member to an image signal, and an imageprocessing device that performs moving image signal processing forprocessing the image signal converted by the image sensing element as amoving image signal and still image signal processing for processing theimage signal as a still image signal, wherein, when the still imagesignal processing is to be executed, the signal processing deviceapplies predetermined limitation upon movement of the opticaltransparent member to a predetermined position, the predeterminedlimitation being not applied when the moving image signal processing isto be executed.

Further, according to the present invention, the foregoing object isalso attained by providing an image sensing apparatus comprising animage sensing element that converts an optical image of an object passedthrough an optical transparent member to an image signal, and an imageprocessing device that performs first signal processing for obtaining animage signal of a first resolution from the image signal converted bythe image sensing element and second signal processing for obtaining animage signal of a second resolution which is higher than the firstresolution from the image signal, wherein, when the second signalprocessing is to be executed, the signal processing device appliespredetermined limitation upon movement of the optical transparent memberto a predetermined position, the predetermined limitation being notapplied when the first signal processing is to be executed.

Furthermore, according to the present invention, the foregoing object isalso attained by providing an apparatus comprising an image recordingdevice that performs image recording of an optical image of an objectpassed through an optical transparent member in a first resolution andin a second resolution which is higher than the first resolution, and acontrol device that performs predetermined control in response tomovement of the optical transparent member to a predetermined positionwhen the image recording in the second resolution is to be executed, thepredetermined control being not performed when the image recording inthe first resolution is to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing an apparatus comprising an image recordingdevice that performs image recording of an optical image of an objectpassed through an optical transparent member in a first resolution andin a second resolution which is higher than the first resolution, and acontrol device for applying predetermined limitation upon movement ofthe optical transparent member to a predetermined position when theimage recording in the second resolution is to be executed, thepredetermined limitation being not applied when the image recording inthe first resolution to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing a control method of an image sensingapparatus comprising the steps of converting an optical image of anobject passed through an optical transparent member to an image signal,and performing moving image signal processing for processing the imagesignal converted by the image sensing element as a moving image signaland still image signal processing for processing the image signal as astill image signal, wherein, when the still image signal processing isto be executed, predetermined control in response to movement of theoptical transparent member to a predetermined position is performed, thepredetermined control being not performed when the moving image signalprocessing is to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing a control method of an image sensingapparatus comprising the steps of converting an optical image of anobject passed through an optical transparent member to an image signal,and performing first signal processing for obtaining an image signal ofa first resolution from the image signal converted by the image sensingelement and second signal processing for obtaining an image signal of asecond resolution which is higher than the first resolution from theimage signal, wherein, when the second signal processing is executed,predetermined control in response to movement of the optical transparentmember to a predetermined position is performed, the predeterminedcontrol being not performed when the first signal processing is to beexecuted.

Further, according to the present invention, the foregoing object isalso attained by providing a control method of an image sensingapparatus comprising the steps of converting an optical image of anobject passed through an optical transparent member to an image signal,and performing moving image signal processing for processing the imagesignal converted by the image sensing element as a moving image signaland still image signal processing for processing the image signal as astill image signal, wherein, when the still image signal processing isto be executed, predetermined limitation upon movement of the opticaltransparent member to a predetermined position is applied, thepredetermined limitation being not applied when the moving image signalprocessing is to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing a control method of an image sensingapparatus comprising the steps of converting an optical image of anobject passed through an optical transparent member to an image signal,and performing first signal processing for obtaining an image signal ofa first resolution from the image signal converted by the image sensingelement and second signal processing for obtaining an image signal of asecond resolution which is higher than the first resolution from theimage signal, wherein, when the second signal processing is to beexecuted, predetermined limitation upon movement of the opticaltransparent member to a predetermined position is applied, thepredetermined limitation being not applied when the first signalprocessing is to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing a control method of an image recordingapparatus comprising the steps of performing image recording of anoptical image of an object passed through an optical transparent memberin a first resolution and in a second resolution which is higher thanthe first resolution, and performing predetermined control in responseto movement of the optical transparent member to a predeterminedposition when the image recording in the second resolution is to beexecuted, the predetermined control being not performed in the imagerecording when the first resolution is to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing a control method of an image recordingapparatus comprising the steps of performing image recording of anoptical image of an object passed through an optical transparent memberin a first resolution and in a second resolution which is higher thanthe first resolution, and applying predetermined limitation uponmovement of the optical transparent member to a predetermined positionwhen the image recording in the second resolution is to be executed, thepredetermined limitation being not applied in the image recording whenthe first resolution is to be executed.

Further, according to the present invention, the foregoing object isalso attained by providing a method of designing an optical system,which is attached to an image recording apparatus capable of recording amoving image and a still image of an optical image of an object passedthrough an optical transparent member, wherein optical property of theoptical system is designed allowable for recording the moving imagewhereas not allowable for recording the still image upon movement of theoptical transparent member to a predetermined position.

Further, according to the present invention, the foregoing object isalso attained by providing a method of designing an optical system,which is attached to an image recording apparatus capable of performingimage recording of an optical image of an object passed through anoptical transparent member in a first resolution and in a secondresolution which is higher than the first resolution, wherein opticalproperty of the optical system is designed allowable for performing theimage recording in the first resolution and not allowable for performingthe image recording in the second resolution upon movement of theoptical transparent member to a predetermined position.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram showing an arrangement of an image sensingapparatus according to a first embodiment of the present invention;

FIG. 2 is a graph showing the relationship between the focal length andeffective image circle diameter;

FIG. 3 is a view showing the relationship between the effective imagecircle and image sensing area;

FIG. 4 is a flow chart showing a still image sensing process in thefirst embodiment;

FIG. 5 is a block diagram showing the arrangement of an image sensingapparatus according to a second embodiment of the present invention;

FIG. 6 is a graph showing the relationship between the focal length andeffective image circle diameter;

FIG. 7 is a view showing the relationship between the effective imagecircle and image sensing area;

FIG. 8 is a flow chart showing a still image sensing process in thesecond embodiment;

FIG. 9 is a block diagram showing an arrangement of an image sensingapparatus according to a third embodiment of the present invention;

FIG. 10 is a flow chart showing a still image sensing process in thethird embodiment;

FIG. 11 is a block diagram showing an arrangement of an image sensingapparatus according to a fourth embodiment of the present invention;

FIG. 12 is a graph showing the relationship between the focal length andresolving power;

FIG. 13 is a flow chart showing a still image sensing process in thefourth embodiment;

FIG. 14 is a block diagram showing an arrangement of an image sensingapparatus according to a fifth embodiment of the present invention;

FIG. 15 is a graph showing the relationship between the focal length andcontrast;

FIG. 16 is a flow chart showing a still image sensing process in thefifth embodiment;

FIG. 17 is a block diagram showing an arrangement of an image sensingapparatus according to a sixth embodiment of the present invention; and

FIG. 18 is a flow chart showing a still image sensing process in thesixth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail in accordance with the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing an arrangement of an image sensingapparatus of the first embodiment. In the first embodiment, an imagesensing apparatus which integrates a video camera, tape recorder, andmemory, and records moving and still images on two different recordingmedia (e.g., a moving image on a tape, and a still image on memory) willbe exemplified.

Referring to FIG. 1, reference numeral 301 denotes a lens; 302, a stop;and 304, an image sensing element comprising a photoelectric conversionelement such as a CCD. Light that has been transmitted through the lens301 passes through the stop 302, and forms an object image on the imagesensing surface of the image sensing element 304. The image sensingelement 304 generates an electrical signal with a charge amountcorresponding to the intensity of light formed on the image sensingsurface.

Reference numeral 303 denotes a zoom lens, the focal length of which isvariable. The focal length of the zoom lens 303 can vary as the positionof the zoom lens 303 moves freely in correspondence with the user'ssetup. Reference numeral 310 denotes a zoom encoder for detecting theposition of the zoom lens 303. Based on the detected position of thezoom lens 303, the focal length can be electrically detected.

Reference numeral 305 denotes a moving image signal processing circuit.Reference numeral 306 denotes a moving image recording unit whichcomprises a VTR or the like and records a moving image on a medium suchas a magnetic tape. Reference numeral 309 denotes a sample & holdcircuit for selectively holding and continuously reading out some ofcontinuous sensed image signals obtained by the image sensing element304. Especially, when a multi-pixel CCD is used, the sample & holdcircuit 309 selects only electrical signals obtained from a given area(e.g., the central portion of the CCD) corresponding to the informationvolume required in, e.g., NTSC from those obtained by the image sensingelement 304. The moving image signal processing circuit 305 converts thesignals selected by the sample & hold circuit 309 into continuous movingimages like signals complying with, e.g., NTSC, and records theconverted signals in the moving image recording unit 306.

Reference numeral 307 denotes a still image signal processing circuitwhich comprises a compressed signal processing circuit or the like thatadopts an image data format such as JPEG. Reference numeral 308 denotesa still image recording unit such as memory. An electrical signalobtained by the image sensing element 304 is passed to the still imagerecording unit 308 that records a still image on a medium such as memoryvia the still image signal processing circuit 307. Furthermore,reference numeral 311 denotes a still image recording control circuitfor controlling still image recording. Details of the circuit 311 willbe described later.

Note that a timing signal generator (not shown) generates and supplies areference timing signal to the image sensing element 304, moving imagesignal processing circuit 305, moving image recording unit 306, stillimage signal processing circuit 307, and still image recording unit 308to synchronously operate them.

Since the apparatus has two recording units, i.e., the moving imagerecording unit 306 and still image recording unit 308, these units canstart and end recording of still and moving images at arbitrary timings.

In general, the effective image range of an optical system including azoom lens becomes narrower with increasing focal length of the zoomlens, or becomes broader with decreasing focal length. In the firstembodiment of the present invention, in an optical system including thelens 301, stop 302, zoom lens 303, and the like, the effective imageranges at all focal lengths do not always cover the entire image sensingarea of the image sensing element 304, but the optical system isdesigned so that effective image ranges obtained at focal lengths largerthan a given focal length cover the entire image sensing area of theimage sensing element 304.

FIG. 2 shows an example of characteristics of a change in effectiveimage range (effective image circle diameter) with respect to the focallength of the zoom lens 303. In FIG. 2, the ordinate plots the effectiveimage circle diameter [mm], and the abscissa plots the focal length [mm]that the zoom lens 303 can be set. Furthermore, reference numeral 701 inFIG. 2 denotes a line indicating the diameter of a circle required tocover all the effective pixels (to be referred to as a “full effectiveimage sensing area” hereinafter) of the image sensing element 304. Also,reference numeral 702 denotes a characteristic curve that indicates achange in effective image circle diameter with respect to the focallength. As indicated by the characteristic curve 702, as the focallength changes from the wide-angle side (W) (i.e., the focal length isshort) toward the telephoto side (T) (i.e., the focal length is long),the effective image circle diameter increases, and when the focal lengthhas exceeded a given focal length fa, the effective image circle coversthe full effective image sensing area of the image sensing element 304.

FIG. 3 explains the state shown in FIG. 2 on the image sensing surface.Referring to FIG. 3, reference numeral 801 denotes the full effectiveimage sensing area of the image sensing element 304, i.e., the full areathat can photoelectrically convert the object image. Reference numeral803 denotes the size of the effective image circle that coverts the fulleffective image sensing area of the image sensing element 304. The focallength at that time corresponds to the point fa in FIG. 2.

When the focal length changes from fa to the wide-angle side, theeffective image circle becomes smaller, as described in FIG. 2, and theeffective image circle at the wide-angle side has a size 804. The objectimage that can be sensed in such case is narrowed down to an area 802.Conversely, when the focal length changes from fa to the telephoto side,the size of the effective image circle exceeds that of the effectiveimage circle 803, and the same operation as in the conventionalapparatus can be done.

Note that the relationship between the size of the effective imagecircle and the focal length is contradictory to the size of the lensoptical system in optical design, and the following choices may be made.That is, in order to attain a size reduction of the lens optical system,the point indicated by the focal length fa is set at the telephoto side,or in order to make the effective image circle effective over a broadfocal length range, the point indicated by the focal length fa is set atthe wide-angle side causing an increase in size of the lens opticalsystem.

Referring back to FIG. 1, the still image recording control circuit 311will be explained below. The circuit 311 checks based on the focallength information obtained by the zoom encoder 310 if the effectiveimage circle diameter at the current focal length set by the user cancover the full effective image sensing area of the image sensing element304. If the effective image circle can cover the full effective imagesensing area, the circuit 311 permits still image sensing; otherwise, itinhibits image sensing. In other words, when the focal length is on thetelephoto side of the point fa on the graph shown in FIG. 2, it isdetermined that the effective image circle covers the full effectiveimage sensing area; when the focal length is on the wide-angle side ofthe point fa, it is determined that the effective image circle does notcover the full effective image sensing area.

The operation of the still image recording control circuit 311 will beexplained below with reference to the flow chart shown in FIG. 4. Thisflow chart is executed at, e.g., every read reference timing of theimage sensing element 304 (step S10). In step S11, the zoom encoder 310reads the current position information of the zoom lens 303 and obtainsthe focal length.

It is checked in step S12 if the current focal length is equal to orlarger than the focal length fa, i.e., if the effective image circlecovers the full effective image sensing area of the image sensingelement 304. If YES in step S12, the flow advances to step S13 to permitstill image recording. On the other hand, if NO in step S12, the flowadvances to step S14 to inhibit still image recording, and the flowadvances to step S17 to end this flow.

If still image recording is permitted in step S13, it is checked in stepS15 if the user has pressed a still image recording trigger button (notshown). If YES in step S15, the flow advances to step S16 to capture animage by storing the current image in the still image recording unit308. On the other hand, if NO in step S15, the flow jumps to step S17 toend this flow.

Note that “still image recording is permitted” in step S13, and “stillimage recording is inhibited” in step S14, but other operations involvedin these operations need not be made. However, when power to the stillimage recording unit 308 is supplied or stopped in correspondence withpermission or inhibition of still image recording, electric power can beefficiently used.

Still image sensing has been explained. In moving image sensing, some ofsignals obtained from the image sensing element 304 are continuouslyrecorded. As described above, since the number of pixels required formoving image display that complies with the existing scheme such as NTSCor the like is smaller than that required for a still image, the sample& hold circuit 309 temporarily selects and holds only image signalsobtained from predetermined pixels of an arbitrary central area of thefull effective image sensing area of the image sensing element 304, andthe held signals are continuously read out and recorded.

For example, when the moving image sensing area is set to be equal to orsmaller than the effective image range at the wide-angle side (area 804in FIG. 3), since the moving image sensing area can fall within theeffective image range irrespective of the focal length, image sensingcan be normally done. Conversely, when the optical system is designed sothat the moving image sensing area (area 802 in FIG. 3) inscribes theeffective image range (area 804 in FIG. 3) at the wide-angle side, thesize of the lens optical system can be minimized.

Second Embodiment

In the first embodiment, still image sensing is permitted or inhibitedin accordance with the relationship between the focal length andeffective image circle. Alternatively, the second embodiment ischaracterized in that the image range in the still image sensing mode ischanged in accordance with the relationship between the focal length andeffective image circle.

FIG. 5 is a block diagram showing an arrangement of an image sensingapparatus of the second embodiment. In the following description, thesame reference numerals denote building components that have alreadybeen explained in FIG. 1, and a detailed description thereof will beomitted. The still image recording control circuit 311 checks based onthe focal length information obtained by the zoom encoder 310 if theeffective image circle diameter at the current focal length set by theuser covers the full effective image sensing area of the image sensingelement 304, in the same manner as that described in the firstembodiment. In the second embodiment, when the effective image circlediameter does not cover the full effective image sensing area, an imagerange that is to undergo a still image signal process is selected via anextraction position control circuit 313 in place of inhibiting stillimage sensing, and only a specific image range is extracted as a stillimage and undergoes a signal process.

This operation will be described in more detail below using FIG. 6. Thegraph shown in FIG. 6 shows the relationship between the focal lengthand effective image circle diameter as in FIG. 2 described in the firstembodiment. In this embodiment, a state wherein the focal length is onthe wide-angle side of fa, and the effective circle diameter is smallerthan that of a circle which covers the full effective image sensing areaof the image sensing element 304, i.e., the diameter assumes a valuesmaller than the value of a line 701 must be noted. In the firstembodiment, still image sensing in this state is inhibited. In suchstate, although image data of the full effective image sensing areacannot be obtained, only an image that can be sensed within theeffective image circle with a diameter indicated by a line 703 in FIG. 6can be captured as a still image.

More specifically, when the focal length becomes smaller than fa, theimage sensing area 802 that inscribes the effective image circle on thewide-angle side shown in FIG. 3 is set as a still image sensing area,and that area is extracted. When only this range undergoes a still imagesignal process, a still image can be sensed although the image area tobe sensed becomes small.

As indicated by the line 703 in FIG. 6, the still image extraction areamay be gradually narrowed down, as indicated by a line 704 in accordancewith the focal length in place of being fixed when the focal length issmaller than fa. Further, when the effective image circle diameterbecomes smaller than that of the circle circumscribing the fulleffective image sensing area (i.e., when the focal length is smallerthan fa), the aspect ratio of the area where data is read out from theimage sensing element 304 as a still image need not always be that ofthe image sensing element 304. For example, the area to be read out fromthe image sensing element may have a square shape as indicated by anarea 805 in FIG. 7 or even circular shape.

The operations of the still image recording control circuit 311 andextraction position control circuit 313 will be explained below withreference to the flow chart shown in FIG. 8. This flow chart is executedat, e.g., every read reference timing of the image sensing element 304(step S20). In step S21, the zoom encoder 310 reads the current positioninformation of the zoom lens 303 and obtains the focal length.

It is checked in step S22 if the current focal length is equal to orlarger than the focal length fa, i.e., if the effective image circlecovers the full effective image sensing area of the image sensingelement 304. If YES in step S22, the flow advances to step S23 to set astill image recording standby state using all pixels. On the other hand,if NO in step S22, the flow advances to step S24 to select pixelscorresponding to the current focal length, thus setting a still imagerecording standby state.

It is checked in step S25 if the user has pressed a still imagerecording trigger button (not shown). If YES in step S25, the flowadvances to step S26 to capture an image by storing the current image inthe still image recording unit 308. On the other hand, if NO in stepS25, the flow jumps to step S27 to end this flow.

As an operation for “selecting pixels corresponding to the focal length”in step S24, a method of setting a look-up table that outputs theposition of a pixel used in image sensing as vertical and horizontalcoordinate positions using the focal length as an argument, a method ofselecting an area based on a computation result from the centralcoordinate position of the image sensing element using a pre-setapproximate expression that uses the focal length as a variable, or thelike may be used. However, the present invention is not limited to thesespecific methods, and any methods may be used as long as an arbitraryarea within the effective image circle can be selected.

The extraction position control circuit 313 informs the still imagesignal processing circuit 307 of the image sensing area to be used inthe still image signal process as the shape, size, distance from thecenter, and the like (, pre-stored as data,) of a figure to be extractedand reads out pixel signals of only that area, thus obtaining a stillimage which does not contain any area outside the effective imagecircle.

Third Embodiment

In the first and second embodiments, still image sensing is inhibited ora pixel signal read area of the still image signal is changed under thecondition in which the effective image circle diameter cannot cover thefull effective image sensing area of the image sensing element 304.Alternatively, the third embodiment does not limit the read operationitself of an image signal, but informs the user that an image sensingarea suffers an optical shadow in the still image sensing mode byproducing an alert.

FIG. 9 is a block diagram showing the arrangement of an image sensingapparatus of the third embodiment. In the following description, thesame reference numerals denote building components that have alreadybeen explained in FIG. 1, and a detailed description thereof will beomitted. Reference numeral 312 denotes an alert device which executes adiscrimination process in accordance with the focal length detected bythe zoom encoder 310, and produces an alert to the user when an opticalshadow is formed in the still image sensing mode. This alert device 312includes a buzzer that produces alert sound, a lamp that makes alertindication, and means for making given display on an electronicviewfinder which is used to confirm a sensed image.

The operation of the alert device 312 will be explained below withreference to the flow chart shown in FIG. 10. This flow chart isexecuted at, e.g., every read reference timing of the image sensingelement 304 (step S30). In step S31, the zoom encoder 310 reads thecurrent position information of the zoom lens 303 and obtains the focallength.

It is checked in step S32 if the current focal length is equal to orlarger than the focal length fa, i.e., if the effective image circlecovers the full effective image sensing area of the image sensingelement 304. If YES in step S32, the flow directly advances to step S35.On the other hand, if NO in step S32, the flow advances to step S34 toproduce an alert indicating that the image sensing circle does not coverthe full effective image sensing area of the image sensing element 304in the still image sensing mode, and the flow then advances to step S35.

It is checked in step S35 if the user has pressed a still imagerecording trigger button (not shown). If YES in step S35, the flowadvances to step S36 to capture an image by storing the current image inthe still image recording unit 308. On the other hand, if NO in stepS35, the flow jumps to step S37 to end this flow.

Fourth Embodiment

The first to third embodiments have exemplified the apparatus whichselects only a local area of the image sensing element 304 by the sample& hold circuit 309 upon moving image recording. Alternatively, thefourth to sixth embodiments to be described later are premised on anapparatus that uses the entire area of the image sensing element 304upon moving image recording.

FIG. 11 is a block diagram showing the arrangement of an image sensingapparatus of the fourth embodiment. The still image recording controlcircuit 311 checks based on the focal length information obtained by thezoom encoder 310 if the resolving power corresponding to the currentfocal length satisfies the required resolving power upon sensing a stillimage, and inhibits still image recording if it does not satisfy.

In the fourth embodiment, in the optical system including the lens 301,stop 302, and zoom lens 303, the resolutions in the entire focal pointdo not always assume values that can satisfy the resolution of the imagesensing element 304, but the optical system is designed so that only arange obtained at focal lengths shorter than a given focal length cansatisfy the resolution of the image sensing element 304, so as to avoidan increase in size of the lens optical system.

The resolving power of the zoom lens 303 corresponding to themulti-pixel image sensing element will be explained below using FIG. 12.FIG. 12 shows a change in resolving power [lines/mm] plotted along theordinate with respect to the focal length [mm] plotted along theabscissa.

In FIG. 12, reference numeral 501 denotes a characteristic curve thatindicates the resolving power of the zoom lens 303 with respect to thefocal length. As can be seen from this curve, the resolving power lowerswith increasing the focal length. Such resolving power characteristicsare determined by balance between the size of the optical system and theresolving power to be obtained at each focal length in optical systemdesign. Designing an optical system with the characteristics shown inthe graph in FIG. 12 attaches importance on the resolving power on thewide-angle side (W) at which the focal length is short, and slightlysacrifices that on the telephoto side (T) at which the focal length islarge, thus attaining a size reduction of the image sensing opticalsystem.

Reference numeral 502 denotes a line indicating the resolving powerrequired in the still image sensing mode. Upon sensing a still image, aresolving power equal to or higher than a threshold value indicated bythe line 502 is required. The resolving power 502 required in the stillimage sensing mode can be uniquely calculated from the resolution (pixelpitch) of the image sensing element 304.

Reference numeral 503 denotes a line indicating the resolving powerrequired in the moving image sensing mode. Upon sensing a moving image,a resolving power equal to or higher than a threshold value indicated bythe line 503 is required. The resolving power 503 required in the movingimage sensing mode can be obtained based on the recording resolution ofthe moving image recording unit 306 or that of the moving image signalprocessing circuit 305, and a smaller one of these values is sued as therequired resolving power 503.

The reason why the required resolving power 502 in the still imagesensing mode and the required resolving power 503 in the moving imagesensing mode are independently set is that a still image requires ahigher resolution of the image sensing element to meet high-imagequality needs, but a moving image can only have a resolution as low asthat of the conventional apparatus since a display device that canreproduce only a resolution as low as that of the conventional apparatussuch as a prevalent monitor that complies with NTSC is used, asdescribed earlier.

As can be seen from the graph shown in FIG. 12, optical characteristicsare locally sacrificed by a size reduction of the optical system inoptical system design. In a range (still image sensing unsuitable range)504 where the optical characteristics are sacrificed and which is notsuitable for sensing a still image on the telephoto side of a focallength fs, a resolution required in the still image sensing cannot beobtained, but there is no problem to perform moving image sensing thatrequires only a low resolution.

The still image recording control circuit 311 will be described below.The circuit 311 checks based on the focal length information obtained bythe zoom encoder 310 if the resolving power of the zoom lens 303 at thecurrent focal length set by the user has a satisfactory value in stillimage sensing. If the resolving power has a satisfactory value, thecircuit 311 permits still image sensing; otherwise, it inhibits stillimage sensing. More specifically, when the focal length obtained by thezoom encoder 310 falls within the still image sensing unsuitable range504, since moving image sensing is possible but a resolution requiredfor still image sensing cannot be obtained, still image sensing isinhibited.

The operation of the still image recording control circuit 311 will bedescribed below with reference to the flow chart shown in FIG. 13. Thisflow chart is executed at, e.g., every read reference timing of theimage sensing element 304 (step S40). In step S41, the zoom encoder 310reads the current position information of the zoom lens 303 and obtainsthe focal length.

It is checked in step S42 if the current focal length is equal to orsmaller than the focal length fs, i.e., if the resolving powercorresponding to the current focal length satisfies the requiredresolving power in the still image sensing mode. If YES in step S42, theflow advances to step S43 to permit still image recording. On the otherhand, if NO in step S42, the flow advances to step S44 to inhibit stillimage recording, and the flow then advances to step S47 to end thisflow.

If still image recording is permitted in step S43, it is checked in stepS45 if the user has pressed a still image recording trigger button (notshown). If YES in step S45, the flow advances to step S46 to capture animage by storing the current image in the still image recording unit308. On the other hand, if NO in step S45, the flow jumps to step S47 toend this flow.

As has been explained in the first embodiment, other special operationsneed not be made in accordance with the operation for “permitting stillimage recording” in step S43 or the operation for “inhibiting stillimage recording” in step S44. However, when power supply to the stillimage recording unit 308 is supplied or stopped in correspondence withpermission or inhibition of still image recording, for instance,electric power can be efficiently used.

The fourth embodiment has exemplified the optical design that sacrificesthe resolving power on the telephoto side at which the focal length islarge. The resolving power may be sacrificed on the wide-angle side atwhich the focal length is short or on both the wide-angle and telephotosides upon designing the optical system, so as to achieve size reductiondesign of the optical system, and this embodiment is also effective insuch case.

Fifth Embodiment

The fourth embodiment adopts the arrangement that pays attention to therelationship between the focal length and optical resolving power.Alternatively, the fifth embodiment pays attention to the relationshipbetween the focal length and optical contrast. Still image sensing maybe inhibited as in the fourth embodiment; however, in the followingdescription, a signal process in the still image sensing mode ischanged.

FIG. 14 is a block diagram showing an arrangement of an image sensingapparatus of the fifth embodiment. In the fifth embodiment as well, asample & hold circuit 316 is provided. However, this sample & holdcircuit 316 thins out photoelectrically converted signals obtained fromthe image sensing element 304 to limit signals to those in apredetermined frequency range in place of making area selection unlikethe sample & hold circuit 309 described in the first to thirdembodiments. Note that the sampling timing can be determined by thefrequency of the moving image signal processing circuit 305 or movingimage recording unit 306.

The still image recording control circuit 311 checks based on the focallength information obtained by the zoom encoder 310 if the contrast atthe current focal length set by the user satisfies the resolution of theimage sensing element in the still image sensing mode. The circuit 311controls the compression ratio of a compression process in the stillimage signal processing circuit 307 via a compression control circuit315 in accordance with the checking result.

More specifically, if the still image recording control circuit 311determines that the contrast at the current focal length set by the userdoes not satisfy the resolution of the image sensing element 304 in thestill image sensing mode, the circuit 311 executes one of a controlprocess (1) that sets a high compression ratio of the still image signalprocessing circuit 307 (sets compression ratio A) to decrease the datasize at the cost of reproducibility of an image in the frequency rangethat cannot be reproduced, and a control process (2) that sets a lowcompression ratio of the still image signal processing circuit 307 (setscompression ratio B) to reproduce the frequency range that is hard toreproduce even by increasing the data size.

When a high compression ratio is set as in the control process (1), thefrequency range that can be reproduced is narrowed down, but the datasize can be reduced. Hence, if the frequency range that can bereproduced is narrowed due to a decrease in optical contrast, thestorage efficiency of the still image recording unit 308 can beeffectively used by executing a signal processing at the highcompression ratio.

By contrast, when a low compression ratio is set as in the controlprocess (2), since the frequency range that can be reproduced isbroadened, still image recording can be done without deteriorating anymore reproducibility in the frequency range in which the opticalcontrast has been attenuated.

Regarding the compression ratio of the still image signal processingcircuit 307 to be controlled by the compression control circuit 315, ahigh compression ratio can be set by; e.g., computing an orthogonaltransform represented by a DCT (discrete cosine transform) or the like,and removing its high-frequency term, and a low compression ratio can beset by keeping the high-frequency term. Note that the present inventionis not limited to such specific compression method, and various otherknown compression methods may be used.

The contrast of the zoom lens 303 corresponding to the multi-pixel imagesensing element will be explained below using FIG. 15. FIG. 15 shows atypical change in contrast of the predetermined resolution at, e.g., thelens central position, and a change in contrast [%] is plotted along theordinate with respect to the focal length [mm] plotted along theabscissa.

In FIG. 15, reference numeral 601 denotes a characteristic curveindicating a change in contrast with respect to the focal length. As canbe seen from the curve 601, the contrast becomes lower with increasingfocal length. By slightly sacrificing the contrast, a size reduction ofthe optical system can be achieved. A decrease in sacrificed contrast isconspicuous especially on the telephoto side at which the focal lengthis large.

Reference numeral 602 denotes a line indicating the first contrastrequired in the still image sensing mode. Still image sensing requiresthe contrast equal to or higher than a threshold value indicated by theline 602. At the contrast equal to or higher than this threshold value,the resolution and element sensitivity of the image sensing element 304can be satisfactorily reproduced. Reference numeral 603 denotes a lineindicating the second contrast at which the process of the still imagesignal processing circuit 307 is to be changed in the still imagesensing mode, and which is used as a reference upon determining a highor low compression ratio in the signal process to be described later.

Reference numeral 604 denotes a line indicating the contrast required inthe moving image sensing mode. When a moving image is sensed, a contrastequal to or higher than a threshold value indicated by the line 604 isrequired.

As can be seen from the graph in FIG. 15, when the size of the opticalsystem is reduced in optical system design, the optical characteristicsare locally sacrificed. In a still image sensing focal length range 605from focal lengths fc1 to fc2, since a contrast required for still imagesensing cannot be obtained, the signal process in the still image signalprocessing circuit 307 is changed to change the compression ratio.Furthermore, in a still image sensing focal length range 606 on thetelephoto side of fc2, the compression ratio is further changed.

The operations of the still image recording control circuit 311 andcompression control circuit 315 will be described below with referenceto the flow chart shown in FIG. 16. This flow chart is executed at,e.g., every read reference timing of the image sensing element 304 (stepS50). In step S51, the zoom encoder 310 reads the current positioninformation of the zoom lens 303 and obtains the focal length.

It is checked in step S52 if the current focal length is equal to orsmaller than the focal length fc1, i.e., if the contrast correspondingto the current focal length satisfies the first contrast required in thestill image sensing mode. If YES in step S52, the flow advances to stepS54 to select a normal compression ratio, thus setting a still imagerecording standby state. On the other hand, if NO in step S52, the flowadvances to step S53.

It is checked in step S53 if the current focal length is equal to orsmaller than the focal length fc2.

If YES in step S53 (within the still image sensing focal length range605 between the focal lengths fc1 and fc2 in FIG. 15), compression ratioA is selected, and the still image recording standby state is set (stepS55). That is, as in the control process (1) described above, a highcompression ratio of the still image signal processing circuit 307 isset, and the data size is reduced by sacrificing the reproducibility ofthe frequency range that cannot be reproduced, thus effectively usingthe storage of the still image recording unit 308.

On the other hand, if NO in step S53 (the still image sensing focallength range 606 on the telephoto side of the focal length fc2 in FIG.15), compression ratio B is selected, and the still image recordingstandby state is set (step S56). That is, as in the control process (2)described above, a low compression ratio of the still image signalprocessing circuit 307 is set to reproduce the frequency range that ishard to reproduce even by increasing the data size, thus recording animage without deteriorating any more reproducibility in the frequencyrange in which the optical contrast has been attenuated.

It is checked in step S57 if the user has pressed a still imagerecording trigger button (not shown). If YES in step S57, the flowadvances to step S58 to capture an image by storing the current image inthe still image recording unit 308. On the other hand, if NO in stepS57, the flow jumps to step S59 to end this flow.

In the fifth embodiment, the focal length range is divided into threeranges, i.e., the still image sensing focal length ranges 605 and 606,and the remaining focal length range as shown in FIG. 15, and signalprocesses are done at different compression ratios. Alternatively, thecompression ratio may be continuously changed as the focal lengthchanges.

Sixth Embodiment

In the fourth and fifth embodiments, the relationship between the focallength and optical resolving power and between the focal length andcontrast have been explained. As another factor that influences thecharacteristics of an optical system, aberration is known. As foraberration, deterioration of its characteristics tends to be emphasizedwith increasing focal length as in the contrast explained with referenceto FIG. 15. Therefore, a reference focal length fr is set foraberration, and discrimination and process are done based on this focallength fr. When the focal length fr is exceeded, still image recordingmay be inhibited, as described in the first embodiment, or the stillimage signal process may be changed (e.g., the compression ratio may bechanged), as described in the fifth embodiment. In the sixth embodiment,an alert is produced.

FIG. 17 is a block diagram showing the arrangement of an image sensingapparatus of the sixth embodiment. In the following description, thesame reference numerals denote building components that have alreadybeen explained in FIG. 1, and a detailed description thereof will beomitted. An alert device 312 executes a discrimination process inaccordance with the focal length detected by the zoom encoder 310, andproduces an alert to the user when optical deterioration will take placein the still image sensing mode. This alert device 312 includes a buzzerthat produces alert sound, a lamp that makes alert indication, and meansfor making given display on an electronic viewfinder which is used toconfirm a sensed image.

The operation of the alert device 312 will be explained below withreference to the flow chart shown in FIG. 18. This flow chart isexecuted at, e.g., every read reference timing of the image sensingelement 304 (step S60). In step S61, the zoom encoder 310 reads thecurrent position information of the zoom lens 303 and obtains the focallength.

It is checked in step S62 if the current focal length is equal to orsmaller than the focal length fr, i.e., if the aberration correspondingto the focal length satisfies the level required in the still imagesensing mode. If YES in step S62, the flow directly advances to stepS64. On the other hand, if NO in step S62, the flow advances to step S63to produce an alert indicating that the aberration does not satisfy anallowable level in the still image sensing mode, and the flow thenadvances to step S64.

It is checked in step S64 if the user has pressed a still imagerecording trigger button (not shown). If YES in step S64, the flowadvances to step S65 to capture an image by storing the current image inthe still image recording unit 308. On the other hand, if NO in stepS64, the flow jumps to step S65 to end this flow.

In the first to sixth embodiments, the still image control circuit 311,extraction position control circuit 313, a discrimination processor ofthe alert device 312, and compression control circuit 315, may beimplemented by, e.g., a microcomputer to execute the flow chartsexplained in the respective embodiments.

It should be noted that, in the above embodiments, still image recordingis inhibited when the focal length is changed across a predeterminedfocal length; however, the present invention is not limited to this, andthe still image recording may not be completely inhibited and merelylimited by, e.g., releasing the inhibition of still image recording by arelease member. Further, instead of inhibiting and limiting the stillimage recording, the position of a zoom lens may be inhibited or limitedso that the focal length does not become the predetermined focal lengthupon still image recording.

Further, the limitation of the still image recording is due todeterioration of resolution corresponding to the focal length in theabove embodiments; however, the present invention is also applicable tocases in which an image is deteriorated due to movement of an opticaltransparent member which passes an optical image of an object, such asdeterioration of an image due to the focus position and a filter.

Furthermore, both of the moving image and still image are recorded on arecording medium according to the above embodiments, however, one orboth of these images may be only displayed or outputted to anotherapparatus and not recorded on a recording medium.

Further, control processes are changed between a moving image and astill image; however, the present invention is not limited to the movingimage and still image, and is applicable to a case of obtaining an imagehaving a first resolution and an image having a second resolution whichis higher than the first resolution using, e.g., a multi-pixel imagesensing element. In this case, the image of the first resolutioncorresponds to the moving image of the above embodiments, and the imageof the second resolution corresponds to a still image of the aboveembodiments.

Other Embodiment

The present invention can be applied to a system constituted by aplurality of devices (e.g., host computer, interface, camera head) or toan apparatus comprising a single device (e.g., digital movie camera).

Further, the object of the present invention can also be achieved byproviding a storage medium storing program codes for performing theaforesaid processes to a computer system or apparatus (e.g., a personalcomputer), reading the program codes, by a CPU or MPU of the computersystem or apparatus, from the storage medium, then executing theprogram.

In this case, the program codes read from the storage medium realize thefunctions according to the embodiments, and the storage medium storingthe program codes constitutes the invention.

Further, the storage medium, such as a floppy disk, a hard disk, anoptical disk, a magneto-optical disk, CD-ROM, CD-R, a magnetic tape, anon-volatile type memory card, and ROM can be used for providing theprogram codes.

Furthermore, besides aforesaid functions according to the aboveembodiments are realized by executing the program codes which are readby a computer, the present invention includes a case where an OS(operating system) or the like working on the computer performs a partor entire processes in accordance with designations of the program codesand realizes functions according to the above embodiments.

Furthermore, the present invention also includes a case where, after theprogram codes read from the storage medium are written in a functionexpansion card which is inserted into the computer or in a memoryprovided in a function expansion unit which is connected to thecomputer, CPU or the like contained in the function expansion card orunit performs a part or entire process in accordance with designationsof the program codes and realizes functions of the above embodiments.

Further, software configuration and hardware configuration disclosed inthe above embodiments may be exchanged.

It should be noted that the present invention includes combinations ofthe aforesaid embodiments or technical elements disclosed therein.

Further, the present invention is applicable to: various types ofcameras, such as a camera using a silver-halide film, alens-exchangeable camera, a single-lens reflex camera, a leaf shuttercamera, and a monitor camera; an image sensing apparatus other thancameras; an image reading apparatus; an optical apparatus; and the like;an apparatus applied to cameras, an image sensing apparatus, an imagereading apparatus, an optical apparatus, and the like; elements formingthe foregoing apparatuses; control method of the foregoing apparatuses;and a computer program product for providing the control method.

The present invention is not limited to the above embodiments andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore to apprise the public of thescope of the present invention, the following claims are made.

1. An image sensing apparatus comprising: (A) an image sensing elementthat converts an optical image of an object passed through an opticaltransparent member, capable of changing a focal length, to an imagesignal; and (B) an image processing device that performs first signalprocessing for obtaining an image signal of a first resolution from theimage signal converted by said image sensing element and second signalprocessing for obtaining an image signal of a second resolution which ishigher than the first resolution from the image signal, and thatcompresses the obtained image signal of the second resolution, wherein,when said second signal processing is to be executed, said signalprocessing device applies predetermined limitation on the basis ofoptical contrast which changes with respect to the focal length of saidoptical transparent member at a position to which said opticaltransparent member is moved, said predetermined limitation being notapplied when said first signal processing is to be executed, thepredetermined limitation including one of using a compression ratiowhich is predetermined for the optical contrast and prohibiting thesecond signal processing, and performed when the optical contrast islower than a predetermined optical contrast.
 2. The image sensingapparatus according to claim 1, wherein said signal processing deviceapplies predetermined limitation when said second signal processing isto be executed and when the focal length is longer than a predeterminedlength corresponds to the predetermined contrast which denotes a minimumoptical contrast required to satisfactorily reproduce the resolution ofthe image sensing element of said image sensing apparatus, saidpredetermined limitation being not applied when said first signalprocessing is to be executed.
 3. The image sensing apparatus accordingto claim 2, wherein said first processing is for a moving image, andsaid second signal processing is for a still image.
 4. The image sensingapparatus according to claim 1, wherein and said predeterminedlimitation is to set an upper limit of the compression ratio on thebasis of the focal length.
 5. The image sensing apparatus according toclaim 4, wherein said first processing is for a moving image, and saidsecond signal processing is for a still image.
 6. A control method of animage sensing apparatus comprising the steps of: converting an opticalimage of an object passed through an optical transparent member, capableof changing a focal length, to an image signal; performing first signalprocessing for obtaining an image signal of a first resolution from theimage signal converted by said image sensing element or second signalprocessing for obtaining an image signal of a second resolution which ishigher than the first resolution from the image signal; and compressingthe image signal of the second resolution, wherein, when said secondsignal processing is to be executed, predetermined limitation is appliedon the basis of optical contrast which changes with respect to the focallength of said optical transparent member at a position to which saidoptical transparent member is moved, said predetermined limitation beingnot applied when said first signal processing is to be executed, thepredetermined limitation including one of using a compression ratiowhich is predetermined for the optical contrast and prohibiting thesecond signal processing, and performed when the optical contrast islower than a predetermined optical contrast.
 7. The image sensingapparatus according to claim 1, wherein, when said second signalprocessing is to be executed, said signal processing device applies afirst compression ratio if the optical contrast is in between the firstoptical contrast which is the predetermined optical contrast and asecond optical contrast which is lower than the first optical contrast,and applies a second compression ratio which is lower than the firstcompression ratio if the optical contrast is lower than the secondoptical contrast.
 8. The image sensing apparatus according to claim 7,wherein the compression ratio continuously changes in accordance withthe optical contrast if the optical contrast is lower than the firstoptical contrast.